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  <h1><a href="/">但行好事，莫问前程</a></h1>
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    <h1 class="title">C语言常用函数</h1>
  

      
        <time datetime="2017-12-20T12:29:44.000Z">2017-12-20</time>
      
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        <h3 id="进程控制相关函数"><a href="#进程控制相关函数" class="headerlink" title="进程控制相关函数"></a>进程控制相关函数</h3><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line">// 获取进程和父进程pid</span><br><span class="line">pid_t getpid(void);</span><br><span class="line">pid_t getppid(void);</span><br><span class="line">// 创建和终止进程</span><br><span class="line">pid_t fork(void);</span><br><span class="line">void exit(int status);</span><br><span class="line">// 等待子进程终止或停止</span><br><span class="line">pid_t waitpid(pid_t pid, int *startusp, int options);</span><br><span class="line">pid_t wait(int *starusp); // wait函数是waitpid的简单版本</span><br><span class="line">// 让进程休眠</span><br><span class="line">unsigned int sleep(unsigned int secs);</span><br><span class="line">int pause(void);</span><br><span class="line">// 在当前进程的上下文中加载并运行一个新程序</span><br><span class="line">int execve(const char *filename, const char *argv[], const char *envp[]);</span><br></pre></td></tr></table></figure>
<a id="more"></a>
<h3 id="普通IO系统调用"><a href="#普通IO系统调用" class="headerlink" title="普通IO系统调用"></a>普通IO系统调用</h3><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">int open(const char *pathname, int flags, int perms);</span><br><span class="line">int close(int fd);</span><br><span class="line">ssize_t read(int fd, void *buf, size_t count);</span><br><span class="line">ssize_t write(int fd, void *buf, size_t count);</span><br><span class="line">off_t lseek(int fd, off_t offset, int whence);</span><br><span class="line">int ioctl(int fd, unsigned long request, ...);</span><br><span class="line">int fcntl(int fd, int cmd, ... /* arg */ );</span><br></pre></td></tr></table></figure>
<h3 id="设置系统的环境变量"><a href="#设置系统的环境变量" class="headerlink" title="设置系统的环境变量"></a>设置系统的环境变量</h3><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">// 获取、添加、删除环境变量</span><br><span class="line">char *getenv(const char *name);</span><br><span class="line">int setenv(const char *name, const char *newvalue, int overwrite);</span><br><span class="line">void unsetenv(const char *name);</span><br></pre></td></tr></table></figure>
<h3 id="字符串相关函数"><a href="#字符串相关函数" class="headerlink" title="字符串相关函数"></a>字符串相关函数</h3><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line">// 返回str的长度</span><br><span class="line">size_t strlen(const char *str);</span><br><span class="line">// 在str所指向的字符串中搜索第一次出现字符c的位置</span><br><span class="line">char *strchr(const char *str, int c);</span><br><span class="line">// 复制字符c到参数str所指向的字符串的前n个字符</span><br><span class="line">void *memset(void *str, int c, size_t n);</span><br><span class="line">// 从src拷贝n个字节到dest</span><br><span class="line">void *memcpy(void *dest, const void * src, size_t n);</span><br><span class="line">// 从str2中复制n个字符到str1中</span><br><span class="line">void *memmove(void *str1, const void *str2, size_t n);</span><br><span class="line">// 比较存储区str1和存储区str2的前n个字节</span><br><span class="line">int memcmp(const void *str1, const void *str2, size_t n);</span><br></pre></td></tr></table></figure>
<h3 id="内存分配相关函数"><a href="#内存分配相关函数" class="headerlink" title="内存分配相关函数"></a>内存分配相关函数</h3><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">// 在对内存中分配长度为size字节的连续区域</span><br><span class="line">void* malloc(unsigned size);</span><br><span class="line">// 给一个已经分配了地址的指针重新分配空间，参数ptr为原有的空间地址，newsize是重新申请的地址长度</span><br><span class="line">void* realloc(void* ptr, unsigned newsize);</span><br><span class="line">void* calloc(size_t numElements, size_t sizeOfElement);</span><br></pre></td></tr></table></figure>
      
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